The present invention relates to a bone grip, and particularly to a bone grip for use in the attachment of the greater trochanter in a total hip replacement operation.
The present inventors have previously developed a range of bone grips for use in hip replacement, and these are described in U.S. Pat. No. 4,269,180. FIG. 1 of the present application is a drawing from that earlier patent, showing a commercially successful embodiment. This is a grip 10 having two parallel side limbs 12 connected by two bridges 14. The limbs curve rearwardly, terminating in upper and lower teeth 16, 18. There are pairs of bores 20 extending completely through the grip, in the regions of the bridges 14.
In a hip replacement operation, part of the greater trochanter may be cut off and has subsequently to be firmly re-attached. For this purpose, it is engaged by a grip 10, which is held in place by cerclage cables which pass through the bores 20 and through holes in the main shaft of the femur. The illustrated grip is for use with two cables. The ends of each cable are passed in opposite directions through the two holes in one of the bridges 14 and tensioned, whereupon the bridge is crimped. The resulting assembly is quite stable, and generally lasts well. However, there are very considerable strains on such a grip, and it is very important that it should hold the trochanter immobile for a period of months. We have found that this design does have a certain tendency to shift in the "vertical" direction (perpendicular to the bridges 14), the motion often approximating to pivoting about one or other of the cables. This is the muscle pull direction, so the forces involved are considerable.
U.S. Pat. No. 4,269,180 discloses also some variants of this design, most of them being generally H-shaped, having a pair of side limbs bridged by a single bridge penetrated by bores. There is also brief mention of a design in the form of a letter A. This is essentially the same as the H-designs, having bores for the cable passing through the bridge (or "cross-bar") of the letter A.